The problem of fogging of sports goggles has been known for many years. In ski goggles this effect takes place when the temperature on the interior of the lens reaches the dew point from the combination of cooling of the lens in contact with the cold air outside, and the flux of moisture from the face into the interior air volume. The fundamental concept to reduce fogging in goggles is to achieve an air temperature in the goggle above the dew point at the surface of the inner lens. The counter actions are to add heat and remove moisture from the interior of the goggle. Attempts at making non-fogging goggles are quite numerous and typically rely on a variety of different techniques.
The following are some examples:
Electric heating of the lens.
Increasing the thermal insulation capability of the lenses by using two lenses with an air gap between them. This reduces the heat flow through the lens and subsequently allows the inner lens surface temperature to come closer to that of the skin surface, thus raising the inner lens temperature above the dew point in the goggle.
Increasing the radiant heat trapping of the goggle lens by coating the surfaces of the lenses facing each other and the outer surface with infrared reflective and low emissivity films. This reduces the lens radiation heat transfer losses. Again this technique subsequently allows the lens surface temperature to be closer to that of the skin surface, thus raising the temperature of the inner lens surface above the dew point in the goggle.
Increasing the radiant heat transfer from the skin to the inner lens, by choosing or coating the inner lens with an infrared absorbing layer on the inner-facing surface of the inner lens. This maximizes the radiant heat transfer from the face to the inner lens, thus allowing the inner lens surface temperature to be closer to that of the skin surface, and raising the temperature of the lens above the dew point in the goggle.
Increasing the air gap between the inner and outer lens. This further decreases the heat loss through the lens and subsequently allows the lens surface temperature to be closer to that of the skin surface, thus raising inner lens surface temperature above the dew point in the goggle.
All three of the thermal insulation techniques mentioned above alone does not result in defogging the goggle because the air just above the surface of the skin and eyes is close to 100% relative humidity and the insulation is not perfect. Thus, the lens is colder than the skin surface and condensation will occur as water diffuses from the skin surface to the lens. Therefore using a thermally resistant lens needs to be coupled to a means of removing the moisture from the skin surface and the volume of air in the interior of the goggle.
The following are several techniques of flowing air into a goggle and transferring heat by airflow:
Use metal foils inside the goggle to transfer heat from the top of the goggle, in which the warmer and lighter air rises, to the incoming air in the bottom of the goggle.
Use various vents that draw or force air through the goggle while the skier is moving.
Heat exchange between incoming air and the outgoing air.
Use a fan to draw air through the goggles.
Use adjustable apertures or lift the face pad to increase or decrease air flow.
The following are techniques to condense water or absorb water vapor in the interior of the goggle:
Use metallic conductors to provide condensation areas inside the goggles.
Use thin lens areas of high heat transfer that condense water.
Use chemical absorbents in a liner on the sides of the lenses, or the lenses themselves, to absorb moisture.
In general, the above techniques are either ineffective in achieving a satisfactory non-fogging effect in the full range of ski conditions or are costly and complex in commercial products.
U.S. Pat. No. 2,612,639, Christensen et al.; xe2x80x9cClosed Goggles Structurexe2x80x9d, describes heat exchangers and condensers for circulation of air and dehumidification. They mention using direct air contact with the face to heat the air in the eyecup cavities. They claim a use of high thermal conductivity material in the condensers, but they do not mention using the high thermal conductivity elements to conduct heat from the user to the air.
U.S. Pat. No. 2,615,162, Christensen et al.; xe2x80x9cCold Weather Gogglesxe2x80x9d, describes using condensers and heat exchangers with closed air circulation in a goggle. They do not describe using heat from the user though conductors to heat the air in the eyecup cavities.
U.S. Pat. No. 2,618,782, Christensen et al.; xe2x80x9cGoggles Structurexe2x80x9d, describes forming inlets and outlets of material of high thermal conductivity. Uses the conductivity of the inlets and outlets to dissipate the heat from the top of the goggle to reduce xe2x80x9cthe absorption of moisture of air in the eye cup cavityxe2x80x9d. This patent also describes insertable air passage-ways: xe2x80x9cAlthough the above outlet structures are formed of flexible copper or other thin metallic conductor material, it will be apparent that rubber or plastic adaptation of this model can be constructed for insertion with the goggles frame.xe2x80x9d This patent does not describe using the heat conducted from the body to heat the inlets or outlets.
U.S. Pat. No. 2,619,643, Christensen et al.: xe2x80x9cCold Weather Gogglesxe2x80x9d, describes using metal heat exchanger to condense the moisture and simultaneously dry and heat the incoming air. They do not mention heating the incoming air through the frame to avoid fogging, nor do they describe using heat transfer from the face contact to the air passages.
U.S. Pat. No. 3,591,864, Allsop: xe2x80x9cNonfog Gogglesxe2x80x9d, describes a double lens for goggles, with a flexible woven wire mesh of high thermoconductivity in the frame. The mesh keeps snow out but is loose enough that moisture condenses.
U.S. Pat. No. 4,290,673, Yamamoto; xe2x80x9cSki Gogglesxe2x80x9d, describes double lens goggles with the space between the lenses being heat insulating. Inner lens has an air port at one end close to the frame and a water-repellent air-permeable filter opposed the air port. No references to wicking or heating incoming air.
U.S. Pat. No. 4,317,240, Angerman et al.; xe2x80x9cSports Gogglexe2x80x9d, describes a single lens goggle with a dual frame design with improved ventilation characteristics.
U.S. Pat. No. 4,584,721, Yamamoto; xe2x80x9cDevice for Use in Helmet for Preventing Fogging by Electric Heatingxe2x80x9d, describes a transparent electroconductive film in the lens used to generate heat with the passing of electric current.
U.S. Pat. No. 4,370,914, Harris; xe2x80x9cEye Protectorsxe2x80x9d, describes goggles with frames comprising rearwardly angled cowls to improve ventilation characteristics.
U.S. Pat. No. 4,707,863, McNeal; xe2x80x9cAnti-Fog Goggle with Foam Framexe2x80x9d, describes goggles with foam frame with air channels incorporated to improve ventilation characteristics.
U.S. Pat. No. 5,018,223, Dawson et al.; xe2x80x9cNon-Fogging Gogglesxe2x80x9d, describes double lens goggles with a vacuum-deposited metal coating film on the outer lens. Body heat radiated through the metal film serves to lower the temperature differential between the outside and the inside of the goggles.
U.S. Pat. No. 5,452,480, Ryden; xe2x80x9cSki Gogglesxe2x80x9d, describes a fan used to exhaust air from the air space between the goggles and a user""s face in order to improve ventilation characteristics.
U.S. Pat. Nos. 5,363,512 and 5,542,130, Grabos, Jr. et al.; xe2x80x9cProtective Goggle and Lens with Adjustable Ventilationxe2x80x9d, describes goggles with adjustable ventilation ports in the frame with a shutter.
U.S. Pat. No. 5,652,965, Crooks; xe2x80x9cNon-Fogging Gogglesxe2x80x9d, describes goggles with screened and unrestricted air ports, which control the amount of air passing through the goggles.
U.S. Pat. No. 5,689,834, Wilson; xe2x80x9cGogglesxe2x80x9d, describes heat sinks used in the goggle structure to dissipate heat inside the goggles. Additional air ventilation ports are disclosed.
U.S. Pat. No. 6,049,917, Ryden; xe2x80x9cAir Injection Sports Goggle and Methodxe2x80x9d, describes a ventilating fan on the top side of a sport goggle which pulls air in through an air injection hole to improve ventilation characteristics.
In order to overcome the shortcomings described above, the present invention discloses a device that combines and optimizes several physical functions into components to achieve the desired effect.
We have found in our research that a human will emit between 0.022 mg/sec (resting) and 0.51 mg/sec (strenuous exercise) of water over an approximate facial surface area of 110 cm2. To remove moisture, air from outside the goggle can flow through the goggle, or moisture can diffuse out. If the relative humidity of the outside air is high, raising the temperature of the air is needed for the airflow to carry moisture from the interior of the goggle. The face transfers heat and moisture to the air surrounding it. If the lens removes heat from the interior of the goggle then more heat needs to be added to the incoming air to avoid reaching the dew point on the surface of the lens.
Typically in skiing conditions the air outside the goggles is near or below the freezing point of water, thus containing little water. In drawing air into the interior of the goggle, the air will be heated by contact with the face, air filter, and lens, and the relative humidity near the wearer""s face will drop below 100%. If the incoming air temperature were brought up to body temperature the air would have a relative humidity below 10%. This air absorbs moisture and flows out of the interior of the goggle.
Some of the features exemplary of, but not limited to, the present invention are summarized below:
The invention uses thermally conductive face contact materials in the face contact gasket to conduct heat from the cheek and nose body contact points to the air flowing into the face-lens volume while impeding the transfer of moisture from the body contact points to the face lens volume. This is a combination of a more thermally conductive face foam gasket with a moisture impermeable or reduced permeability barrier on the interior facing side. This gasket is then thermally coupled to surfaces of thermally conductive honeycomb air inlets, and or grooved or finned surfaces on the interior of the goggle frame. The face gasket can transfer heat internally by conduction, radiation, evaporation, condensation, convection and/or the like.
The face gasket includes, but is not limited to, the following features:
Open cell foam or cavities with interior sealed walls or channels in thermal contact with the face and the heat transfer surfaces. The body moisture will vaporize, diffuse, and condense on the adjacent goggle frame transferring heat to the frame or air heat transfer surfaces.
Thermally conductive metal, rubbers, and plastics incorporated in the face gasket.
Liquid-filled face gasket that transports heat by the high conductivity of the liquid or convection of the liquid.
Liquid and vapor-filled face gasket bladder that is a heat pipe to vaporize fluid at the body surface and condense the fluid at contact with the frame or heat transfer surfaces.
Radiant cavities in the gasket such that, by having high emissive interior surfaces, radiant heat is emitted and absorbed from the face contact to the frame of the goggle or the air heat transfer surfaces.
Air convection cells that transport heat from the body surface to the frame or air heat transfer surfaces. These could be channels in the face gasket that allow air to flow in the gasket between the face and the frame, but not into face lens region, to transport heat.
Form a face gasket, which moves condensed water on the interior surfaces under and near the gasket to the outer perimeter, by wicking, to be evaporated to the atmosphere.
The face gasket has the functions of moving water away from the surface of the skin outside the interior of the goggle and transferring heat to the goggle frame and heat transfer surfaces, while simultaneously sealing the goggle to the face to prevent snow from entering the interior of the goggle.
Create airflow inlet and outlet channels that have low impedance to flow while maximizing their heat transfer and snow blocking abilities to create a convective airflow regardless of outside air flow conditions.
This feature is essentially trying to optimize the natural convection within the goggle or a so-called xe2x80x9cchimney effectxe2x80x9d. Air inside the face-lens volume is warmed and becomes buoyant. The air rises and exits out through outlet channels at the top of the goggle and is replaced by cold, outside air which is drawn into the face-lens volume through inlet channels at the bottom of the goggle. The lighter warm air removes moisture from the interior of the goggle as it rises, while the enclosure of the goggle maintains some snow blocking abilities.
One preferred embodiment uses a thermally conductive honeycomb, chevrons, or slotted inlets and outlets that are thermally connected to the face gasket. The effective diameter and length of the channels are sized to minimize air flow drag and maximize heat transfer while still blocking snow.
With a high enough air flow our research has shown that goggles in almost all cold weather conditions will remain clear. We have found, by testing commercially available goggles, that the typical snow filter foam has cell sizes and thicknesses that present a very high resistance to natural convection in goggles. The critical scaling parameter for air flow through these small air inlets (laminar flow) is air flow resistance per unit area, which is proportional to the length of the channels and inversely proportional to the square of the aperture size. In the present invention, the sizes of the inlet and outlet channels are such that natural convection within the goggle is achieved.
Form air flow channels that have a low flow impedance, block snow ingress, move fluids, such as but not limited to, liquid water, away from the face-lens volume and shield from air flow effects outside the goggle.
Our research has shown that heat transfer from the body to the air at the top of the goggle does not help significantly to clear the lens. On the other hand, it does help to avoid condensation in the top outlet channel and make a small contribution to the chimney effect thereby allowing moisture laden warm air vent out to the atmosphere. The other critical function of the top outlet channels are to prevent snow or liquid water from falling into the goggle. The lower air inlet channels have a larger effect on air flow and moisture removal. A typical problem will be condensation at the outlet which can drip back into the goggle. A xe2x80x9crain gutterxe2x80x9d needs to be formed to move the condensed moisture away from the face-lens volume. Wicking or a hydrophilic channel to move water out of the face-lens volume is used in this invention. The lower air inlet is expected to have less snow impacting it and liquid water can exit.
Coatings on the air flow channels for optimum heat transfer, wetting and absorption properties.
The air flow channels can be coated with hydrophilic materials such as, but not limited to, solid polymer electrolytes that cause snow to melt and form a wetted film. The melted water may then be channeled out to a wicking system. The wetting coating prevents coalescence of water droplets and avoids condensed water blocking or dripping down into the goggle through the air channels. This helps make the channel surfaces sticky to snow and the liquid, thus making it easier to flow a film of water across them to the wicks. The flow channels may also act, to some degree, as moisture absorbing surfaces until they become saturated.
The coatings may have high emissivity (black) to also allow radiant heat to be transferred through the channel and the goggle and to avoid outside visible light being transmitted through the channel to the user. Absorption of ambient light also adds thermal energy to the air channels to help warm air and remove moisture.